The invention envisages the devices of the type described in Patent EP-A-0 519 850 (TECHNIFOR). It will be recalled that, in these devices, the marking tool, of the micro-percussion type, is mounted axially at the end of a swivelling rod of which the opposite end penetrates inside a fixed casing through an articulated linkage capable of being formed both by a universal joint and by a simple ball-and-socket joint.
For controlling the orientation of the tool-holder rod, the casing contains an actuation mechanism which comprises two telescopic jacks oriented parallel to each other to act on two arms fixed radially on the rod and disposed perpendicularly to each other. One of the two elements of each jack is coupled by a ball-and-socket joint to the casing, whilst the other element is itself connected, by a ball-and-socket joint, to the end of the radial arm which corresponds thereto.
In one of the embodiments described in the prior document mentioned above, the two actuation jacks are oriented parallel to the axis of symmetry of the swivelling rod, being coupled to the wall of the casing opposite the one which bears the articulated linkage. It will be appreciated that, if this rod is retained angularly against any rotation along its axis, such an actuation mechanism ensures, under excellent conditions, control of the displacement of the tool.
However, it should be noted that such an arrangement further presents a substantial drawback, in that, further to the geometry of the assembly, any control exerted by one of the two jacks necessarily involves a correcting action applied to the other jack, and this even in the case of the device being used for marking rectilinear lines. Such permanent correction complicates the electronic equipment used for controlling the actuation mechanism.
It is an object of the present invention to overcome this drawback which, in practice, is not insignificant.